Apparatus for and method of producing continuous foamed plastic bunstock

ABSTRACT

Apparatus and method are described for improved production of foamed bunstock in continuous length. A generally U-shaped moving mold is utilized within which a thermosetting foam mix is deposited and the bunstock is then formed as a continuous block. This moving mold is configured along a critical portion of its length to conform as closely as practical to the inverted mirror image of the profile defined by the characteristic curve of percent of foam rise as a function of time for any selected foam mix composition. A weir arrangement is employed to control the travel of foam mix while this is still highly liquid. The objective is to maintain a condition of hydrostatic balance throughout the body of developing foam from the point of mix lay down to the point of foam gellation. Features of the invention reside in the concept of and means for changing the weir configuration and mold profile to achieve that condition of operation in which various forces acting on and in the developing foam mix produce the aforesaid hydrostatic equilibrium. By so doing greater flexibility is achieved in terms of ability to adapt a given production installation to handle different foam compositions, production rates, bunstock dimensions and shapes, with better uniformity of foam density and cell isotropicity than heretofore commercially practical.

United States Patent [19] Porter June 3, 1975 APPARATUS FOR AND METHODOF PRODUCING CONTINUOUS FOAMED PLASTIC BUNSTOCK [75] Inventor: LawrenceC. Porter, Palos Verdes Penninsula, Calif.

[73] Assignee: The Upjohn Company, Kalamazoo,

Mich.

22 Filed: July 23,1973

21 Appl. No.: 381,923

[52] U.S. Cl. 264/41; 264/46; 264/51; 264/54; 425/4 [51] Int. Cl B29d27/04 [58] Field of Search 264/41, 46, 51, 54; 425/4, 425/115 [56]References Cited UNITED STATES PATENTS 3,476,845 11/1969 Buffet a1.264/54 3,560,599 2/1971 Ferstenberg 264/41 Primary Examiner-Lewis T.Jacobs Attorney, Agent, or FirmSteward & Steward [57] ABSTRACT Apparatusand method are described for improved bunstock is then formed as acontinuous block. This moving mold is configured along a criticalportion of its length to conform as closely as practical to the invertedmirror image of the profile defined by the characteristic curve ofpercent of foam rise as a function of time for any selected foam mixcomposition. A weir arrangement is employed to control the travel offoam mix while this is still highly liquid. The objective is to maintaina condition of hydrostatic balance throughout the body of developingfoam from the point of mix lay down to the point of foam gellation.Features of the invention reside in the concept of and means forchanging the weir configuration and mold profile to achieve thatcondition of operation in which various forces acting on and in thedeveloping foam mix produce the aforesaid hydrostatic equilibrium. By sodoing greater flexibility is achieved in terms of ability to adapt agiven production installation to handle different foam compositions,production rates, bunstock dimensions and shapes, with better uniformityof foam density and cell isotropicity than heretofore commerciallypractical.

lllllllllllllulllllllfll APPARATUS FOR AND METHOD OF PRODUCINGCONTINUOUS FOAMED PLASTIC BUNSTOCK BACKGROUND OF THE INVENTION Thisinvention relates to casting of continuous length foamed bunstock from athermosetting fluid mix, more especially polymeric isocyanates such aspolyurethane foams, but is likewise applicable to other expandable,themosetting foam mixes. The invention relates in particular toimprovements in apparatus for and method of manufacturing such foamproduct of improved density gradient and cell isotropicity.

Foamed plastic bunstock is used extensively in the manufacture ofbedding (mattresses, pillows), furniture and automotive upholstery,thermal and sound insulation, and the like. Selfgassing polyurethanemixes are currently used predominantly. For many of these applicationsit is not practical to mold or cast the polyurethane foam directly inits desired final shape or form, especially, where physicalcharacteristics of maximum uniformity of density, resiliency and thelike are important. Usually it is more economical, and sometimes it isunavoidably necessary from a practical standpoint, to produce theproduct in large cast buns or billets of standard modular dimension, andthen cut these into sections of desired shape. Bun molding has beencommercially practiced for some time, both on a batch or individualbun-forming basis, and more recently in a continuous process wherein thefoam mix is deposited in a moving mold to produce a bun of uninterruptedlength. This is then sawed, sliced, etc., into appropriate lengths forultimate product fabrication, as well as interim convenience ofhandling, shipping and storing.

In order to avoid waste in converting the ascast product to its finalshape, one of the important considerations is to obtain a bun that has aflat top or minimum cresting or bread-loaf configuration; in otherwords, is of as nearly rectangular cross section as possible. Thisbread-loafing effect is a characteristic result of methods heretoforeused in producing buns. Obviously if there is a substantial crest orhump in the top surface of the bun as produced, there will be asignificant scrap loss upon skiving or cutting the billet into slabs toget flat, parallel surfaces. Since the foamed plastic generally has arelatively high unit value and since commercial production of the foamruns in the millions of pounds annually, any substantial scrap lossaggravates the cost of the finished product.

If there are splits, voids, bubbles and other discontinuities in thebody of the foam stock, which has also been a common difficulty,portions of the foam block containing these must be cut out, thusproducing further scrap loss. Additionally, nonisotropic cellularformation in the stock impairs the physical properties of the finishedproduct, so a high degree of uniformity in the shape and size and axisorientation of the foam cells produced is accordingly desirable.

Although it might appear to be an easy solution, for ensuring adimensionally uniform product, simple to confine the developing foam bysuitable fixed molding or shaping means, this is not in fact readilyaccomplished, especially in practical commercial practice involvingproduction of as much as several million pounds of product monthly in asingle plant. During the development of the foam several actions andreactions take place simultaneously, and in some cases competitively.That is, there is generation of a gas to produce the foamed cellularproperties, and at the same time there is a polymerization reactiontaking place, leading to gellation or rigidifieation of the walls of thecells to impart the desired degree of resiliency and body in theproduct.

Prior attempts to produce foamed bunstock in a continuous mannergenerally involve depositing a reactive foam mix on a lower conveyorsurface, such as a continuous paper web drawn over a stationary bed orpour board. Side restraints are also used to complement the lowersurface, forming a U-shaped mold, looked at in cross section, ofextended length. See for example U.S. Pat. No. 3,152,361. In order toget a finished foam bun of uniformly rectangular cross section,smoothing or ironing belts, aprons, rollers and the like have beenapplied to the surface of the advancing foam during its development.Examples of this are seen in U.S. Pat. Nos. 3,123,856, 3,553,300 and3,655,311. This results in a tendency towards densification orcompacting of the product, particularly at its upper surface, which isundesirable and this non-specification portion must usually be cut offand discarded.

To get around this, other attempts have been made to produce continuousflat top bunstock without any vertical confinement, using synchronouslymoving side conveyors complementing the lower conveyor surface andexerting a lateral effect on the developing foam bun. Some of thesesystems are quite complicated mechanically and troublesome to adjust andmaintain. See for example U.S. Pat. Nos. 3,091,811 and 3,719,734; alsoBritish Pat. Nos. 1,225,968 and 1,235,915.

Potentially, what appeared for a while to be one of the more promisingdevelopments in continuous foamed bunstock production was a so-calledupsidedown process in which the lower conveyor element forming thebottom of the moving U-shaped mold is trained to move downward, relativeto horizontal side elements, during that portion of the run where themaximum expansion occurs. The desired objective was to keep the uppersurface of the developing foam at a substantially constant, horizontallevel, while allowing the body of the foam to expand downwardly to meetthe declining portion of the conveyor run. Typical examples of thisapproach are seen in U.S. Pat. Nos. 3,325,823 and 3,560,599. It ispostulated that by causing the bottom of conveyor to descend relative tofixed side wall elements, there is a reduction of the frictionalrestraint at the interface of the foam stock and side conveyor elements,and that this would reduce the tendancy to form a relatively largeradius in the bunstock at the intersection of the side and top surfaces.Unfortunately this prior teaching has not afforded a practical solutionon account of both technological and economic problems with theproposals advanced. As a result, the industry has turned to thosemechanically more complex systems of attempting to provide side liftingarrangements for the developing foam, as for instance those shown inU.S. Pat. No. 3,719,734 and the British patents mentioned above. Notonly is there substantial equipment expense and added maintenanceinvolved, there must also be a willingness to compromise on the qualityof product obtained. For example, socalled tin splits can becomecritical, forcing an operator to resort to mix compositions that are notas favorable from the standpoint of foam resiliency, sag resistance,thermal properties or uniform density. There is the further disadvantagein that a given installation does not have much latitude or flexibilityto permit use of different foam mix compositions, rates of production orambient operating conditions from those for which the equipment wasspecifically designed.

Another area of difficulty encountered in prior systems has been that ofpreventing washback or undercutting of the developing foam on the pourboard. This problem arises in part by uneven distribution in theadvancing foam mix of portions of substantially different age; that is,portions of the liquid mix deposited on the conveyor at materiallydifferent times. The usual manner of depositing the mix on the movingconveyor is to transverse a mixing head back and forth across the widthof the conveyor, laying down a zig-zag path of the mix on the advancingconveyor web. If the mixing head traverse rate is not properlycoordinated with the throughput rate of liquid mix, the conveyor speedand the pitch of the pour board beneath the mixing head, substantialdeviation may arise in average age of the liquid mix in any transversesection taken along the pour board downstream of the mixing head.Additional problems arise from portions of the mix, which have begun tofoam, floating backwards against the direction of conveyor travel, whileunreacted (non-foaming) portions of the liquid are carried forward andmixed with other portions downstream in which the foaming reaction hasalready progressed much further.

SUMMARY OF THE INVENTION Generally speaking the invention providesapparatus for and a method of producing foamed plastic bunstock thatwill permit a flexibility of operating parameters not afforded by priordevelopments in this art.

The inventive concept is directed toward making possible, underpractical large scale production conditions, the achieving of a set ofoperating conditions which is adjustable to match the risecharacteristics of any selected foam mix composition, whereby a body orpool of liquid and semi-liquid mix is maintained in a state ofhydrostatic balance between the mixing head and the point wheregellation finally occurs.

This result is obtained by apparatus which incorporates means foradjustment, as presently more fully discussed, such that for any givenset of operating conditions (e.g., mix composition, throughput, bunstocksize, shape, component temperature condition, etc.) the moving mold canbe set to provide a receptacle for the foam mix whose configurationlengthwise of the mold formed by the advancing conveyor closelyapproximates the inverted mirror image of the rise profile of theselected foam mix under the given operating conditions. It is a furtherfeature of the invention that changes in mold configuration provided bythe conveyor may be introduced without interruption of production bymaking small but reasonable incremental changes both in formulation andin apparatus. Changes in formulation can be controlled by a system suchas that described in the previously mentioned US. Pat. No. 3,655,311,while the means of effecting physical adjustment of apparatus tocompensate for such changes is the subject of this invention.Practically this is accomplished by apparatus for, and a method of,making one or more adjustments which characteristically include:

a. Providing a pour board, including upstream, intermediate, anddownstream sections, the latter hereinafter called the surfboard portionfor convenience of nomenclature. These various sections are adjustablyinclinable in relation to complementary side elements of a movingU-shaped mold, to provide a path which descends at different rates orslopes in the direction of foam travel. Means is also incorporated forincreasing and decreasing the length of the surfboard and changing itssurface contour; and

b. Providing damming or weir means which extend across the pour board atselectively adjustable positions upstream of the surfboard, whose heightand configuration, both longitudinally and transversely, are alsoselectively adjustable.

The characterizing novel features just mentioned are preferably used incombination, but some benefits of the invention will be obtained byindividual use of them, as will be apparent hereinafter. Other,conventional adjustment capabilities include conveyor speed,longitudinal and vertical positioning of the mixing head, and rate oftraverse of the mixing head.

The invention is illustrated more specifically with reference to theaccompanying drawings in which:

FIG.-1 is a side elevational view of a conveyor system for continuousproduction of polyurethane foam bunstock;

FIG. 2 is a top plan view of a portion of the apparatus shown in FIG. 1;

FIG. 3 is a cross sectional view taken on line 3-3 of FIG. 2;

FIG. 4 is a schematic drawing showing the relative relationship betweenthe characteristic rise curve of a typical polyurethane foam mix andcorresponding positions on the apparatus where the rising foamcharacteristics are encountered;

FIG. 5 is an enlarged cross sectional view, schematically depicting aportion of the pour board with rising foam thereon;

FIG. 6 is a perspective view of an integrated pour board unit;

FIGS. 7 and 8 are sectional views in side elevation of modified pourboard arrangements useful in the apparatus.

FIGS. 9 through 12 are representative cross-sections of bunstock withtypical imperfections encountered with prior production methods.

The apparatus in FIG. 1 of the drawings illustrates one manner ofincorporating the inventive concept in a practical machine.

Mixing head 10 is suitably suspended from bridge 12 to permit it to bemoved back and forth across the width of the bun-forming line by anysuitable power means (not shown). Liquid components of the foam mix aredelivered under pressure to mixing head 10 through flexible hoses l4,and the liquid mix is distributed by pour spout 16 of the head. Meansfor proportioning and premixing the multiple components of a typicalcommerical polyurethane mix are described in US. Pat. No. 3,655,311,previously mentioned. Spout 16 delivers a stream of the mix onto acontinuously advancing paper web (more fully described below) which istraveled over a composite pour board, indicated generally at 18, whoseupstream section provides a flat surface 20 beneath mixing head 10,which leads into a contoured intermediate section 22. This later sectionleads in turn to the surfboard section 24, referred to above, providedby a portion of the run of an endless conveyor 26. A main conveyor 28,consisting of an endless belt or series of transverse slats, is disposedto provide a substantially horizontal run extending from the lower endof surfboard 24 to a carry off and/or storage conveyor 30. Sideconveyors 34, each carrying a continuous web of paper or similar sheetstock 38, are disposed vertically at the side edges of the surfboard andmain conveyor. A tunnel 39 of conventional type encloses the bun linethroughout much of the zone where the bun is developed.

The several pour board and conveyor sections just described provide alower supporting surface forming part of a U-shaped moving mold in whichthe foamed bunstock is cast and allowed to develop. The sides or legs ofthe U-shaped mold are provided at the upstream end of the apparatus by apair of side rails 32 which laterally flank the upstream portion of thepour board. Conveyors 34 serve as continuations of the side rails 32.Sheet stock 36 is trained over the respective pour board and mainconveyor surfaces, and similar webs 38 are disposed along opposite sideconveyors 34, to form the moving U-shaped mold by which the foamedproduct is actually carried until developed. As seen more especially inFIG. 2, web 36 forming the bottom element of the mold is foldedmarginally upwardly, as at 36a by rails 32 as it is fed off its supplyroll onto the pour board, and thus forms a shallow trough in the regionin which the liquid mix is first deposited by the mixing head 10. Thesefolded margins 36a meet with the side sheets 38 in the region of theintermediate portion 22 of the pour board, and are brought intoface-toface contact with side sheets 38 which thereafter serve as themoving side walls of the bunstock mold.

The product is delivered to carry-off conveyor in continuous form as agenerally rectangular block which is sawed into appropriate lengths forsubsequent fabrication into finsihed products. Prior to this the bottomand side webs, 36, 38 may be stripped from the bunstock.

Referring now more specifically to the schematic illustration in FIG. 4,a plot is made of the characteristic rise profile of a selectedpolyurethane foam mix against a time axis, and direct comparison of thisis made with longitudinal positions on the foam line, shownschematically beneath the plot. As discussed above, bottom sheet 36 ispulled over the countoured surface of the pour board section of the bunline, and the fluid resin mix is deposited on this sheet from pour spout16. This corresponds to zero time on the foam rise plot. At this pointthe pour board surface 20 is typically disposed at a small angle ofdeclination to the horizontal, commonly from 2 to 4which helps toprevent floatback of developing foam, contra to the conveyor travel. Asthe liquid mix is carried forward onto intermediate section 22 of thepour board, reaction taking place within the mix causes a transition tooccur from an all-liquid phase system to a mixed liquid-gas system. Thisphase change is readily observable and is conventionally referred to asthe cream line although it will in fact usually be a zone rather than asharply defined line of demarcation. It has been found important tostabilize the position of this cream line longitudinally of the pourboard, otherwise there will be a tendency for the formation of voids orother discontinuities in the body of the finally developed foam.Depending on the method of fluid mix lay down and distribution, waveaction will develop in the pool of liquid deposited on the pour board,which will give rise to a poorly defined cream line, leading tochannelling or selective undercutting wherein unreacted liquid isinterspersed with the foam arriving on the surfboard.

In order to give better control of the position and form of cream line,the invention includes providing damming formations or weirs in theintermediate section 22 of the pour board. In the particularillustration in FIG. 4, a multiple stage weir arrangement embodyingtransverse slats 40, 42 whose spacing and height can be adjusted forparticular operating conditions, such as rate of throughput, conveyorspeed, pour board angle and particular mix composition. More on thiswill be discussed hereinafter.

With the initiation of gassing, as evidenced by the appearance of thecream line, the volume of the liquid mix begins to expand significantly.This expanding condition is represented by the increased slope in theprofile of the foam rise curve, and continues until the mix becomessufficiently gelled or polymerized to be at least self-supporting. Thisslope may be relatively constant, as in the solid line showing, or itmay be curvilinear, as in the dotted line showing. In order toaccommodate this volumetric increase, the surfboard section 24 of thepour board is tilted down from the horizontal at an increased angle, andprovision may also be included for changing its contour, so that thevolume of the mold defined by section 24 and the side walls increases indirect proportion to the increase in foam volume as it progressesthrough this section of the conveyor. Thus the upper surface of the foamis maintained substantially horizontal from the breakover point B, justdownstream of the weir, throughout the rest of the travel of the foam.By this means, a hydrostatically balanced condition is maintained in thepool of developing foam on the pour board-surfboard configurationbetween point B and until gellation occurs, and the foam simply lies inthe mold provided for it. Under such condition there is no requirementfor flow to take place in the developing foam from one section or regionof the foam body toward some other section or region which has beentemporarily depleted. Such depletion is usually caused by adhesion ofthe foam to the side webs 38 under those conditions where thedeclination of surfboard 24 produces a mold volume change that is notequal to the change taking place in the foam body itself atcorresponding points along the conveyor. This situation will prevailunder any operating condition other than one unique condition in asystem of fixed design. That one unique condition will of course bedetermined by all of the variables involved, including polymercomposition, temperatures, rates of throughput at the mixing head,conveyor speed, physical lengths and pitch angles of the pourboardsurfboard configuration, and'bun size.

Since each particular set of operating conditions will produce differentinstantaneous conditions in the developing foam in the period betweeninitial laydown and final gellation, the pour board and surfboardconfigurations must be made adjustable if this hydrostatically balancedcondition is to be achieved. The present invention is directed moreparticularly to practical means for accomplishing this.

Referring again to FIGS. 1 and 2, the angle of declination in theinitial section of the pour board at the point of fluid mix laydown isadjusted by suitable jack means 44, 46 at the rearward and forward endsof a platform 48 on which the upstream and intermediate sections 20, 22of the pour board are supported. Typically this angle is about 2 to 4 tothe horizontal, but can vary from a few degrees negative to as much as 7positive. The terminal or surfboard portion 24 of the pour board isformed by an endless belt conveyor which is trained over a series ofrolls 50, 52, 54 and 56. Roll 50 locates the upper end of the surfboardimmediately contiguous to the breakover point, corresponding to point Bin FIGS. 4 and 5, at the end of the intermediate portion 22 of the pourboard, while roll 52 determines the lower end of the surfboard 24. Itwill be noted that roll 50 is journalled on platform 48, while roll 52is journalled on the framework of the main conveyor 28. A telescopingplatform 51 bridges the distance between rollers 50 and 52, and ispivotally attached at its opposite ends to frame members to providesupport for conveyor belt 26. Thus the angle of declination of surfboard24 can be changed by raising or lowering platform 48, while the lengthof surfboard 24 can be changed by moving main conveyor 28 toward or awayfrom the first portion of the apparatus. For this reason, main conveyor28 is supported on rollers 60 and a screw jack 62 is interposed betweenthe conveyor frame and the support for the pour board platform. Roll 56is a take-up roll to allow for increase or decrease in the length ofsurfboard 24, while roll 58 serves as a driving roll for impartingforward motion to the conveyor belt from a driving source 59. The latteris used also to supply driving power to main conveyor 28 throughsprocket 29, the driving connection including shafting and adifferential transmission 61 to keep bottom web 36 synchronized with thetravel of side webs 38 when screw jack 62 is actuated. If the contour ofsurfboard 24 is also to be adjustable, platform 51 is composed ofarticulatable sections, and a suitable fluid operated ram 53 or theequivalent are used to set the contour.

In addition to the control provided in the pour board configurationdownstream of breakover point B, there are the damming weirs upstream ofthis point. As illustrated in FIGS. 1 and 2, weirs 40, 42 consist ofslats disposed transversely of the conveyor in intermediate section 22of the pour board. These weirs are adjustably mounted on this section ofthe pour board so that they can be individually or simultaneously movedupstream or downstream and fixed in selected position. The mounting ofthese weirs on the board also allows for changing their elevation abovethe pour board. Bottom web 36 is drawn over the weirs, forming spaceddams with a slight depression between them.

One of the major problems facing the operator of a continuous foam bunline is to coordinate the numerous variables confronting him to get asatisfactory product. Changes in chemical composition of the mix, as forexample to eliminate splits in the bun, or to try to improve the flattop characteristics, may resultin causing the natural position of thecream line to shift so radically that it goes beyond the breakoverpoint. Liquid mix of a different age from other more mature surroundingmix will then exist on the surfboard section of the pour board. Theresulting foam product will have non-uniform density, and isotropicityof the cell structure will likewise deteriorate. This difficulty ofholding the cream line in proper position can be largely if notcompletely overcome by the provision of one or more weirs. At lowthroughput rates of the order of 100-200 pounds per minute, and at slowconveyor speeds, a single weir may be sufficient to stabilize the creamline for tion, component temperature and mixing head traverse rates.Generally however a series of at least two weirs has been found muchmore satisfactory. With such an arrangement, the first weir acts like awave breaker, damping the oscillatory washing effect produced by thereciprocation of the mixing head in delivering the liquid mix. Thedissipation of the wave action provided by the first weir is thensupplemented by the next weir which helps to trap, temporarily, a poolof liquid between the weirs. Since there is some mild agitation ormixing action imparted to the liquid in the pool due to the drag effectof bottom web 36, the momentarily trapped increment of mix becomes morehomogeneous in terms of average age. Furthermore, the tendency of thefoam developing at this point to float back toward the mixing head isrestrained, a problem encountered if a low pitch angle (under 3) of thepour board is needed. The presence of a second, downstream weir isgenerally needed at production rates of 200-600 lbs/min. and at thehigher pour board pitch angles (above 3) to restrain the foam fromflowing past the breakover point until it has aged and expandedsufficiently to be ready for release to the surfboard section.

In actual practice, the initial phase change in the mix producing thecream line phenomenon will appear as a band or zone of substantialwidth, as much as a foot or two in length for example, depending on mixformulation, conveyor speed, etc. Under typical operating conditions,adjustment is made to cause this cream line or zone to straddle aninitial rise of a composite weir 41, as shown schematically in FIG. 5,while a second rise in the weir serves to hold the developing foam fromsliding down the surfboard. The second rise will release the foamgradually as it expands and builds up a sufficient head above the weir.Through longitudinal placement of the weir, and adjustment of itsheight, the amount of hydrostatic head that must be developed by thefoam before it passes the breakover point can be controlled to give theproper timing in respect to the rise configuration which it is desiredto have take place on the subsequent surfboard section 24. When allconditions are properly set, a visual indication of this is evidenced bythe fact that the level of the upper surface of the foam stays virtuallyflat and level, or parallel to the main conveyor, from the time itleaves the breakover point B to the end of the conveyor.

For many practical applications it is convenient to employ a unitarypour board section having weir elements integrally formed in its uppersurface, such as the unit shown in FIG. 6, cut from a slab of moldedrigid foam stock to provide a flat upstream portion 72 which leads intoa first riser 74, a step 76, a second riser '78 and a terminal portion80.

This unit, when placed on platform 48 (FIG. 1) and provision made forshifting it forward or backward along the conveyor axis, can be designedto satisfy a family of mix formulations and production rates to meetmost foam density and resiliency objectives. Such a unit provides foradjusting the distance between the pour point P on surface 72 and thefirst weir 74 to adapt the upstream portion of the pour board to riseprofile changes or throughput changes, for example. Although this willalso change the relative position of the second weir 78 and breakoverposition to the pour point, satisfactory operation can be achieved byproper selection of the height and spacing of the weirs, especially ifcorrelation of the distance of the breakover position B to surfboardsection 24 is made by shifting either or both unit 70 and mixing head10. For flexible foam compositions of the common commercial densityranges, for example, of from around 1.2 to over 1.8 pounds per cubicfoot, a weir height of about I /zinches for each weir, and a spacing ofabout 2 feet between them gives excellent control for line capacities upto as much as 600 pounds per minute of foamed product.

Further refinement of the pour board configuration control is obtainedby superimposing a number of foam slabs, or the equivalent, asillustrated in FIG. 7. The composite pour board section 90 there shownconsists of a base layer 92 and superimposed layers 94, 96, each ofshorter length than the other to provide a stepped configuration. Boltand nut or other clamping means 98, passing through slots 100, 102 inthe respective layers, permit longitudinal adjustment of the layersrelative to each other, thereby enabling the spacing between the weirs104, 106 to be changed.

A further alternative is illustrated by unit 110 of FIG. 8, in which abase 112 has inflatable sections 114, 116 superimposed on it. Ducts 118,120 lead to the interiors of the respective sections for communicationto a source of fluid pressure which may be regulated to give more orless inflation of the sections. To provide some adjustment of weirspacing, each section 1 14, 116 is divided into compartments, eachof-which communicates through a respective duct 118 or 120 to the sourceof fluid pressure and may accordingly be individually infiated.

It is usually desirable to slope the weir faces in the di' rection oftravel to conform more closely with the contour assumed by bottom web 36when it is drawn over the surface of the pour board. Similarly, at thetrailing end of the integrated pour board section, this is tapered tomake a smooth, more gradual transition to the surfboard section. A flap122 (FIG. 8) of flexible sheet plastic or fabric may also be secured tothe tail of the unit to overlie the gap between this section and thesurfboard portion, as a furhter means of providing a smoother transitionat this point.

Prior approaches to continuous molding of bunstock, in which the productis as nearly rectangular in section as possible and yet has adequateisotropic cell structure to meet physical end-use specifications, have,as mentioned previously, been directed primarily to ways of manipulatingor bodily moving the rising foam to physically compel it to assume aparticular shape. Not only has the apparatus needed for this beenmechanically complex and expensive to house, build and maintain, theobjectives of desired bun configuration and properties are inadequatelyobtained. By contrast, this invention is directed toward eliminating, tothe extent possible, physical molding restraints imposed on the risingfoam itself, relying almost exclusively on gravity. This is done byproviding a mold configuration that can be tailored to therisecharacteristics of the selected polymer mix while the apparatus isoperating. There is thus provided the ability fora bunstock lineoperator to quickly achieve a state of balance between the volumeincrease occuring in the mix and the volume of the mold at any givencross section through the developing bun. That is, the developing foamis not itself required to do work, either in moving resilientlysupported panels, aprons, conveyors, etc. to accommodate the expansion,or in shifting portions of the foam body to fill in voids left in otherportions which develop because of non-coincidence of natural,unrestrained foam volume and volume of the mold at the instant suchincrement of foam resides in that section of the mold. This is thehydrostatically balanced condition spoken of earlier.

Physical evidence of the efficacy of the invention is provided bypractical experience from experimental operation. Problems with bunshape configurations are correctable through employment of theinvention, and without interruption of the production line. For example,formation of a bun having a cross section such as that represented inFIG. 9 is commonly due to too great a slope of the surfboard section ofthe pour board. Such undulated upper surface configuration will beobservable in the foam as it passes over the surfboard while still in asemifluid state. Correction can be made by incrementally lowering thepour board platform, as by means of jacks 44, 46 seen in FIG. 1, todecrease the slope of surfboard 24. Conveyor speed is another parameterthat can be manipulated to slow down the foam progress and thus bringthe developing foam volume into balance with the mold volume; butconveyor speed change alone cannot be used to rectify the situationcompletely, since this has side effects on cream line position,breakover point, and timing of the gellation point with respect totransition of the bun from the surfboard to the main conveyor.Adjustability of the surfboard contour and pitch thus provides aflexibility of control not encumbered by so many of the problems arisingfrom conveyor speed or formulation change.

FIG. 10 represents a bun cross section typically encountered in whichthe bread-loafing effect spoken of earlier is apparent. This is again aprobable indication of an unbalance between developing foam volume andmold volume (the latter being in this case too slow, i.e. the surfboardpitch being too low). FIG. 10 also illustrates discontinuities in thetexture of the bun cross section, in the form of bubbles and voids.Another variant of the bubble problem is shown in FIG. 9 wherein linesof bubbles appear immediately below the troughs in the top of the bun.These bubbles are generally the result of non-uniformity in agecondition of the foam mix. Conventional steps taken to correct for thiscondition have been to change conveyor speed and mix formulation. Thisis partially effective but usually introduces other problems. However,by adjusting the weir arrangement provided by this invention, muchgreater latitude in operation is made possible without encountering thedifficulties of conveyor speed or formulation change.

Still another problem is represented in FIG. 1 l which illlustrates abun of good rectangular section but in which lateral splits appear. Thiscondition usually indicates that the timing of the transition of thebunstock from the surfboard to the main conveyor is improperlycoordinated with substantial completion of gellation in the bun. Iftransistion occurs after gellation has occurred, the bending of thebunstock as it leaves the surfboard produces stresses resulting in suchtears, since the stock has not developed sufficient strength at thatpoint to resist the stress. To correct for this, conventional practicehas been to speed up the conveyor slightly to get the bun off thesurfboard before gellation is so nearly complete, or to change thecatalyst ratio in the mix. Again, however, changing these parametersintroduces other problems. Thus the capability of the inventionapparatus to increase or decrease the length of the surfboard providesanother capability for introducing a correction without affecting otherparameters.

FIG. 12 illustrates a bun of desirable flat top characteristicobtainable with proper surfboard configuration; but the presence of thebubble formation, indicating channeling of liquid and foam (i.e.,incomplete homogenization) at a late stage in the development of thebun, seriously detracts from the marketability of the product. Use ofproper weir arrangements as taught herein will generally eliminate thisproblem, without creating others. In fact, the weir arrangements of thisinvention may be used to good advantage in conventional foam lines,quite independently of the articulated surfboard portion of thisinvention. This is especially true when trying to operate conventionalfoam line equipment at higher throughputs, of the order of 500-6OOpounds per minute of foam mix. At such rates so much liquid must bedeposited that conveyor speeds up to around feet per minute may berequired, using steeper angles of conveyor declination, and longconveyor lengths between the pour point and cream line. Operation ofconventional equipment under such conditions becomes very critical andthe slightest upset in the process can result in a mess of foam-floodedequipment and expensive down-time and clean-up operations. Use of theweir arrangement of this invention affords a relatively simple means ofalleviating some of the criticality in such operations, givingsignificant improvement in the economic operation of conventionalequipment.

The apparatus here shown for purposes of illustrating the invention isobviously capable of substantial modification within the scope of theconcept disclosed. The particular surfboard conveyor arrangement shownis not critical in its detail, since other arrangements can be designedto perform the same functions. Other weir arrangements can likewise beemployed, as for example weir configurations which are curved or slantedrather than rectilinear, as specifically shown. Such modification is ofuse in directing the flow of liquid mix into selected areas transverselyof the conveyor to compensate for channeling or striation occuringnaturally due to method of lay down of the mix. The weirs provide ameans of introducing a correction for this at a point in the productionof the bun where the material is still highly fluid, rather than byattempting to compensate for channeling at some later point through theuse of adjustable mold sides, etc. At such time, the mix has undergonesubstantial increase in viscosity and tends to resist redistributionwithout adverse effect on the texture, etc., of the product.

The following claims are accordingly intended to comprehend all suchchanges and modifications which fall within the true scope andequivalency of the concept herein disclosed.

What is claimed is:

1. A method of producing longitudinally continuous foamed bunstock froma reactive liquid polymeric mix to provide a continuous length expandedcellular product of substantially rectangular cross section, uniformdensity and cell isotropicity, which comprises the steps of advancing acontinuous conveyor surface along a predetermined path of travel, saidconveyor surface comprising a lower supporting portion and separateupstanding portions on laterally opposite sides of said lower portionand defining together a generally trough-like moving mold for thedeveloping foam product; depositing reactive liquid polymer mix on saidconveyor surface at a first point in its path of travel; advancing saidconveyor surface in a generally horizontal plane with reacting liquidmix thereon to a second point along its path of travel; adjustingflow-impeding means disposed across said conveyor path intermediate saidfirst and second points to produce a continuous pooling of said liquidmix therebetween to establish a stable cream line in the pooled liquidtransversely of the path of travel and immediately ahead of said secondpoint;

adjusting the path travelled by the lower portion of said conveyorbetween said second point and a third point downstream thereof toconform said path approximately to the mirror image of thecharacteristic rise profile of the particular polymer mix developed inthe time interval of conveyor travel between said second and thirdpoints, wherein said third point is adjustably positioned tosubstantially coincide with the point of maximum rise of the polymerfoam; and

thereafter continuing said conveyor surface travel from said third pointthrough a curing zone to a point of discharge for the finished expandedcellular product.

2. The method as defined in claim 1, which includes the step of varyingthe longitudinal positioning of said liquid flow-impeding meansintermediate said first and second points.

3. The method as defined in claim 1, which includes positioning a seriesof liquid flow-impeding means intermediate said first and second point.

4. The method as defined in claim 3, which includes varying the heightof the successive liquid flowimpeding means.

5. The method as defined in claim 1, which includes adjusting the heightof said flow-impeding means.

6. The method as defined in claim 1, which includes the step of varyingthe length of travel of said lower conveyor surface between said secondand third points in the path of travel.

7. The method as defined in claim 1, wherein the longitudinalpositioning of said liquid flow-impeding means is varied intermediatesaid first and second points and wherein the slope of said lowerconveyor surface portion relative to said opposed lateral portions isvaried between said second and third points in the path of travel.

8. The method as defined in claim 7, wherein the length of travel ofsaid conveyor surface between said second and third points is varied.

9. The method of producing longitudinally continuous foamed bunstockfrom a reactive liquid polymeric mix to provide a continuous lengthexpanded cellular product of substantially rectangular cross section,uniform denisty and cell isotropicity, which comprises the steps ofadvancing a continuous conveyor surface along a predetermined path oftravel, said conveyor surface comprising a lower supporting portion andseparate upstanding portions on laterally opposite sides of said lowerportion and defining together a generally trough-like moving mold forthe developing foam product;

13 depositing reactive liquid polymer mix on said conveyor surface at afirst point in its travel; advancing said conveyor surface in agenerally horizontal plane with reacting liquid mix thereon to a secondpoint along its path of travel;

adjusting the path traveled by the lower portion of said conveyorbetween said second point and a third point downstream thereof toconform approximately to the mirror image of the characteristic riseprofile of the particular polymer mix developed in the time interval ofconveyor travel between said second and third points, wherein said thirdpoint is adjustably positioned to substantially coincide with the pointof maximum rise of the polymer foam; and

thereafter continuing said conveyor surface travel from said third pointthrough a curing zone to a point of discharge for the finished product.

10. The method as defined in claim 9, which includes the step of varyingthe length of travel of said lower conveyor surface between said secondand third points in the path of travel.

11. A method as defined in claim 9, which includes the step of varyingthe rate of downward shifting of said lower supporting portion of saidconveyor surface relative to said lateral portions between said secondand third points in the path of conveyor travel.

12. A method of producing longitudinally continuous foamed bunstock froma reactive liquid polymeric mix, which comprises the steps of advancinga continuous conveyor surface along a predetermined path of travel froma point of liquid mix lay down to a point of discharge of finishedproduct, said conveyor surface comprising a lower supporting portion andseparate upstanding portion on laterally opposite sides of said lowerportion and defining together a generally trough-like moving mold forthe developing foam product;

depositing reactive polymer mix on said conveyor surface at a firstpoint comprising said point of liquid mix lay down;

advancing said conveyor surface in a generally horizontal plane withreacting liquid mix thereon to a second point along its path of travel;

adjusting weir means disposed transversely of the conveyor pathintermediate said first and second points and causing said lower supportconveyor portion to travel over said transversely disposed weir means tothereby provide a variably positionable flow-impeding rise in its pathof travel between said points.

1. A method of producing lonGitudinally continuous foamed bunstock froma reactive liquid polymeric mix to provide a continuous length expandedcellular product of substantially rectangular cross section, uniformdensity and cell isotropicity, which comprises the steps of advancing acontinuous conveyor surface along a predetermined path of travel, saidconveyor surface comprising a lower supporting portion and separateupstanding portions on laterally opposite sides of said lower portionand defining together a generally trough-like moving mold for thedeveloping foam product; depositing reactive liquid polymer mix on saidconveyor surface at a first point in its path of travel; advancing saidconveyor surface in a generally horizontal plane with reacting liquidmix thereon to a second point along its path of travel; adjustingflow-impeding means disposed across said conveyor path intermediate saidfirst and second points to produce a continuous pooling of said liquidmix therebetween to establish a stable cream line in the pooled liquidtransversely of the path of travel and immediately ahead of said secondpoint; adjusting the path travelled by the lower portion of saidconveyor between said second point and a third point downstream thereofto conform said path approximately to the mirror image of thecharacteristic rise profile of the particular polymer mix developed inthe time interval of conveyor travel between said second and thirdpoints, wherein said third point is adjustably positioned tosubstantially coincide with the point of maximum rise of the polymerfoam; and thereafter continuing said conveyor surface travel from saidthird point through a curing zone to a point of discharge for thefinished expanded cellular product.
 1. A METHOD OF PRODUCINGLONGITUDINALLY CONTINUOUS FOAMED BUNSTOCK FROM A REACTIVE LIQUIDPOLYMERIC MIX TO PROVIDE A CONTINUOUS LENGTH EXPANDED CELLULAR PRODUCTOF SUBSTANTIALLY RECTANGULAR CROSS SECTION, UNIFORM DENSITY AND CELLISOTROPICITY, WHICH COMPRISES THE STEPS OF ADVANCING A CONTINUOUSCONVEYOR SURFACE ALONG A PREDETERMINED PATH OF TRAVEL, SAID CONVEYORSURFACE COMPRISING A LOWER SUPPORTING PORTION AND SEPARATE UPSTANDINGPORTIONS ON LATERALLY OPPOSITE TROUGH-LIKE MOVING MOLD FOR DEFININGTOGETHER A GENERALLY SIDES OF SAID LOWER PORTION AND
 2. The method asdefined in claim 1, which includes the step of varying the longitudinalpositioning of said liquid flow-impeding means intermediate said firstand second points.
 3. The method as defined in claim 1, which includespositioning a series of liquid flow-impeding means intermediate saidfirst and second point.
 4. The method as defined in claim 3, whichincludes varying the height of the successive liquid flow-impedingmeans.
 5. The method as defined in claim 1, which includes adjusting theheight of said flow-impeding means.
 6. The method as defined in claim 1,which includes the step of varying the length of travel of said lowerconveyor surface between said second and third points in the path oftravel.
 7. The method as defined in claim 1, wherein the longitudinalpositioning of said liquid flow-impeding means is varied intermediatesaid first and second points and wherein the slope of said lowerconveyor surface portion relative to said opposed lateral portions isvaried between said second and third points in the path of travel. 8.The method as defined in claim 7, wherein the length of travel of saidconveyor surface between said second and third points is varied.
 9. Themethod of producing longitudinally continuous foamed bunstock from areactive liquid polymeric mix to provide a continuous length expandedcellular product of substantially rectangular cross section, uniformdenisty and cell isotropicity, which comprises the steps of advancing acontinuous conveyor surface along a predetermined path of travel, saidconveyor surface comprising a lower supporting portion and separateupstanding portions on laterally opposite sides of said lower portionand defining together a generally trough-like moving mold for thedeveloping foam product; depositing reactive liquid polymer mix on saidconveyor surface at a first point in its travel; advancing said conveyorsurface in a generally horizontal plane with reacting liquid mix thereonto a second point along its path of travel; adjusting the path traveledby the lower portion of said conveyor between said second point and athird point downstream thereof to conform approximately to the mirrorimage of the characterIstic rise profile of the particular polymer mixdeveloped in the time interval of conveyor travel between said secondand third points, wherein said third point is adjustably positioned tosubstantially coincide with the point of maximum rise of the polymerfoam; and thereafter continuing said conveyor surface travel from saidthird point through a curing zone to a point of discharge for thefinished product.
 10. The method as defined in claim 9, which includesthe step of varying the length of travel of said lower conveyor surfacebetween said second and third points in the path of travel.
 11. A methodas defined in claim 9, which includes the step of varying the rate ofdownward shifting of said lower supporting portion of said conveyorsurface relative to said lateral portions between said second and thirdpoints in the path of conveyor travel.
 12. A method of producinglongitudinally continuous foamed bunstock from a reactive liquidpolymeric mix, which comprises the steps of advancing a continuousconveyor surface along a predetermined path of travel from a point ofliquid mix lay down to a point of discharge of finished product, saidconveyor surface comprising a lower supporting portion and separateupstanding portion on laterally opposite sides of said lower portion anddefining together a generally trough-like moving mold for the developingfoam product; depositing reactive polymer mix on said conveyor surfaceat a first point comprising said point of liquid mix lay down; advancingsaid conveyor surface in a generally horizontal plane with reactingliquid mix thereon to a second point along its path of travel; adjustingweir means disposed transversely of the conveyor path intermediate saidfirst and second points and causing said lower support conveyor portionto travel over said transversely disposed weir means to thereby providea variably positionable flow-impeding rise in its path of travel betweensaid points.
 13. The method as defined in claim 12, which includesimposing a series of flow-impeding rises between said first and secondpoints.